The commercial processing of photographic materials produces seasoned solutions containing silver ions. Environmental regulations restrict the discharge of such solutions to within acceptable concentrations of silver that are much less than the concentrations of silver in the seasoned solutions. Various methods of removing silver from these solutions have been attempted, with varying expense and success.
The most common types of silver recovery in current use include the use of steel wool recovery cartridges ("CRC's"), electrolysis, and ion exchange. CRC's are messy and not always reliable. Electrolysis is expensive, requires significant maintenance, and can result in ammonia gas generation. Ion exchange is costly and impractical for smaller photoprocessors and minilabs. Another silver recovery process employs sodium sulfide as a precipitating agent, but this process can result in the evolution of toxic fumes.
Another approach has been use a silver complexing agent to remove silver from particular photographic effluent solutions.
UK 1411985 describes a method of removing silver ions from photographic bleach-fix solutions using precipitating compounds such as dimercaptotriazoles.
U.S. Pat. No. 3,778,368 describes a method of removing a harmful metal such as silver from waste water using trimercapto-s-triazines or their salts.
A problem with these approaches is that separate separation facilities and equipment are required for the individual solutions, which can be inconvenient and expensive, particularly for small photoprocessing labs or minilabs. Furthermore, these processes do not provide a process capable of recovering silver from minilab effluent solutions such as photographic stabilizers to obtain a sufficiently low silver concentration acceptable for discharge to the environment.
It is an object of the invention to provide a process for recovering silver from seasoned photographic solutions, including stabilizers, capable of lowering silver concentration in the solutions to within acceptable environmental discharge limits.